1. Field of the Invention
The invention relates to a method of erasing, in a document data processing device, a stored information pattern on a rewritable data carrier that is accessible by a data processing facility of the document data processing device, the document data processing device having primary processes for processing document data that may be stored on the data carrier, and secondary processes for erasing stored data, through overwriting a selected storage area of the data carrier by a shredding pattern.
2. Discussion of the Background Art
Magnetic hard disks and other more or less similar storage facilities are increasingly vulnerable to reading of confidential data that is stored thereon. A first type of attack may occur through a hacker “entering” the facility via a data network. Such interference may be countered by relatively simple operations, such as encrypting the data before storing them on the internal hard disc, deleting the entry of the particular data file in the file administration of the carrier, or preferably overwriting the data.
A more serious type of attack may occur after physical removal of such a disk from a Personal Computer, a Digital Access Controller associated to a printing facility, or others. Deleting the file administration of the carrier will then be to no avail.
Reformatting the carrier or over-writing the data by a so-called shredding pattern provides improved security, but there are techniques for detecting bit patterens that have been overwritten. A single “data shredding” run is therefore insufficient when deletion of certain data is really important.
Overwriting data with a plurality of shredding runs involving multiple different bit patterns, further to be called: shredding patterns, is generally considered as an effective policy, wherein the construction of the shredding patterns should be appropriate to the intended degree of security.
The data carrier can be based on various different writing/storing technologies, such as magnetic, magneto-optical, optical such as in a rewritable CD, and others. Usually, the geometrical storage organization is based on a kind of track, that may be a cylinder, a spiral, a straight line, or others. The storage physics is based on some kind of remanence property of the storage substrate.
In particular, United States Patent Application Publication No. 2002/0181134 A1 to Bunker et al. discloses the application of user-selectable shredding patterns. The present inventors have recognized that this technology may offer enough protection against infringers, but that the long time required by the overall shredding will keep the data processing proper, e.g. printing, stalled for an often highly needed time interval and may therefore severely degrade system performance.
Furthermore, an overall discussion of shredding operations and other related items is given in P. Gutmann, “Secure Deletion of Data from Magnetic and Solid-State Memory”, Sixth USENIX Security Symposium Proceedings, San José, Calif. USA, Jul. 22-25, 1996, pp. 77-90.